Non-Invasive Positive Pressure Ventilation (NIPPV) is a form of treatment for breathing disorders which can involve a relatively higher pressure of air or other breathable gas being provided to the entrance of a patient's airways via a patient mask during the inspiratory phase of respiration, and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration. In other NIPPV modes the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment.
Continuous Positive Airway Pressure (CPAP) treatment is commonly used to treat breathing disorders including Obstructive Sleep Apnea (OSA). CPAP treatment continuously provides pressurized air or other breathable gas to the entrance of a patient's airways via a patient mask at a pressure elevated above atmospheric pressure, typically in the range 3-20 cm H2O. CPAP treatment can act as a pneumatic splint of a patient's upper airway.
CPAP treatment can be in a number of forms, including the maintenance of a constant treatment pressure level, alternating between two different constant levels in synchronism with the inspiratory and expiratory phases of respiration (“bi-level CPAP”), and having an automatically adjustable and/or a computer controlled level in accordance with a patient's therapeutic needs. In all of these cases there is a need for control over the pressure of air or breathable gas supplied to the patient mask.
Breathable gas supply apparatus used in CPAP and NIPPV treatments broadly comprise a flow generator constituted by a continuous source of air or other breathable gas generally in the form of a blower driven by an electric motor. A pressurized supply of air or other breathable gas can also be used. The gas supply is connected to a conduit or tube, which is in turn connected to a patient mask (or nasal prong) which incorporates, or has in close proximity, a vent to atmosphere for exhausting exhaled gases, such as carbon dioxide. To vary the flow supplied to the patient during inspiration and expiration, a valve member can be used, such as the valve member disclosed in U.S. patent application Ser. No. 09/598,053. For example, a cammed rotatable member can be used to permit a large flow during patient inspiration, and a relatively small (or substantively no) flow during patient expiration. However, this type of valve arrangement may be disadvantageous since during the patient expiration, when the valve member does not permit a significant, if any flow, the blower, which is upstream of the valve member, may be choked. Stated differently, flow through and from the blower may temporarily stop if the valve member is positioned to prevent or substantially prevent flow to the patient, e.g., when the patient is in the expiration phase of the breathing cycle. When inspiration resumes and the valve member rotates so as to permit flow or more flow to the patient, the fan or impeller associated with the blower may require a few revolutions (e.g., two) in order to reinstate flow through the impeller to the conduit and to the patient. As such, the response time of the CPAP apparatus when changing from the expiration to the inspiration may be delayed.
Treatment pressure of the air or other breathable gas can be controlled by speed control of the electric motor driving the blower of the flow generator. An example of a related art flow generator using a speed controlled blower is illustrated in FIG. 1. Conventional flow generator 110 is comprised by a chamber 112 that is segregated from a housing 114 of the flow generator 110. The housing 114 houses control circuitry (not shown) associated with the flow generator 110. The flow generator 110 is further comprised by a motor 116 driving an induced flow centrifugal turbine (impeller) 118, which induces the flow of air or breathable gas by an air inlet 120 to pass the air or breathable gas under pressure by an air outlet 122 to the air delivery tube (not shown) and so to the mask (also not shown). The turbine 118 has radially directed impeller blades 124. The alternate use of axial fans is known also in CPAP apparatus.
For typical CPAP treatment, the blower motor must be able to change its operational speed quickly. This results in the need to supply additional electrical power during times of operational speed increases. Disadvantages associated with rapid transitions in motor speed are, for example, noise, vibration, blower choking, and increased thermal dissipation requirements, in addition to increased power requirements.
Treatment pressure can alternatively be controlled by driving the electric motor of the blower at a constant speed, and venting or bleeding-off excess air from the output side of the blower. An example of this type of related art pressure control is shown in FIG. 2. A turbine 118 is connected to a plenum chamber 130 by a supply pipe 132. The plenum chamber 130 has a controllable spill valve 134 operable to indexingly open and close an opening 136 in the chamber wall to allow the venting of air to atmosphere so as to achieve the desired output pressure at an air outlet 138. Consequently, venting can be associated with excessive noise when the treatment pressure is adjusted. Additionally, it is difficult to maintain precise treatment pressure regulation and to maintain a high maximum flow rate, due in part to the large volume of plenum chamber 130. Imprecise treatment pressure regulation can lead to patient discomfort.
FIGS. 3A and 3B illustrate a prior art treatment pressure control using a bleeding valve 140 in fluid communication with blower 150 that is operated by a mechanism 142 situated within the flow path 144. In this embodiment, the mechanism 142 operates primarily in either an open position 146 (FIG. 3A) or a closed position 148 (FIG. 3B), resulting in imprecise, abrupt treatment pressure regulation. Additionally, the mechanism 142 situated in the flow path 144 can impede flow and cause noise, and can introduce into the flow path 144 odors and/or other contaminants generated during the operation of the mechanism 142. This results in patient discomfort and decreased patient compliance with treatment.
Noise and/or patient discomfort decrease patient compliance with treatment of breathing disorders. Therefore, there is a need in the prior art for an improved apparatus that increases patient compliance with treatment by reducing disadvantages including noise emissions and imprecise treatment pressure regulation. There is also a need to provide a valve arrangement that can prevent choking of the blower and/or improve the speed and/or response time when the ventilation changes from the expiration mode to the inspiration mode.